1. Field of the Invention
The present invention relates to data storage devices. In particular, the present invention relates to improving performance of suspension assemblies in data storage devices.
2. Related Art
In data storage devices, data is typically stored in tracks on a memory medium. To access the data, the head is positioned within a track of the memory medium while the medium moves beneath the head. In many storage devices, the head is positioned by an actuator assembly that includes a motor that rotates one or more actuator arms. Each actuator arm supports one or two suspensions that each support a head/gimbal assembly. Typically, a suspension includes three distinct areas: a boss plate area that connects to the actuator arm, a spring area that provides a vertical spring force to bias the head toward the medium, and a load beam that extends from the spring area to the head/gimbal assembly. A spring force provided by the suspension is designed to allow the head to follow height variations on the surface of the medium without impacting the medium or moving too far away from the medium. Typically, it is desired that the spring area be more elastic or flexible than the remainder of the suspension. However, if the spring area or the remainder of the load beam is too elastic and compliant the load beam will tend to bend and resonate in response to various forces applied to the suspension.
A suspension is capable of resonating in three different axes: bending, torsion, and lateral or sway. The bending mode of vibrations depends on bending stiffness. To increase bending modes of vibrations, the bending stiffness can be increased and inertia reduced. Bending stiffness, however, cannot simply be increased without weighing other factors. By increasing bending stiffness too much, gram load sensitivity is increased due to vertical translation of the suspension. This is undesirable because it makes the tolerances of the head stack assembly more critical.
Similarly, to improve torsional modes of vibrations, an increase in torsional stiffness and a reduction in inertia are required. But torsional stiffness and bending stiffness are coupled together because both derive from the same spring portion of the load beam. In order to reduce torsional inertia, mass needs to be reduced as well as the distance from the torsional axis to the center of gravity. This can be achieved by reducing the width of the suspension, but reducing the suspension width decreases lateral bending or sway mode resonance. Also, narrowing of the suspension width and other reductions in mass can change the vertical stiffness, which may require additional re-working of the head stack assembly to achieve the desired gram load to the head/gimbal assembly
Control of resonant induced vibrations have become very important as disc drive technology continues to increase in complexity and performance requirements. For example, many high performance disc drives run at 15 k RPM or higher, causing significant windage forces within the disc drive. Also, there is an increasingly higher number of bits being packed into every square inch of the disc drive surface, leading to a higher number of tracks per inch and a reduced track width. As a result, suspensions are more susceptible to slider off-track motion and other mechanical resonant vibrations that lead to reduced servo bandwidth and reduced track following capabilities of the disc drive.
One way of minimizing the effects of resonant induced vibrations in the suspension is to provide a dampening feature. Dampening features added to various portions of the suspension assembly may reduce the vibrations by stiffening the suspension in certain axes. Known dampening methods may provide desired dampening characteristics, but typically significantly alter the mass of the suspension or change the preload force applied to the head of the suspension.
A dampening feature for a suspension assembly that provides dampening of vibrations in specific axes of the suspension while maintaining other characteristics of the suspension, such as preload forces to the head, would be an important advance in the art.